KR960016702B1 - Process for producing stabilized zirconia from zircon sand - Google Patents

Abstract

The stabilized zirconia is produced by the steps of: adding and mixing a CaO as a stabilizing agent and carbon as a reducing agent to a zircon sand to be measured with a molar ratio of CaO/zircon sand of 0.5-0.8, carbon/zircon sand of 2.0-4.0; preparing a briquette from the mixture; heat-melting the briquette by heat plasma of high temperature for 2-7 minutes, cooling, and then recovering, crushing a produced solid product.

Description

Process for producing stabilized zirconia from zircon sand

1 is a manufacturing process chart for producing stabilized zirconia from zircon sand by the wet method.

2 is a manufacturing process diagram for producing stabilized zirconia from zircon sand in accordance with the present invention.

3 is a schematic diagram showing a working state in which briquette samples are placed in a water-cooled copper crucible and melted by high temperature plasma.

4 is an X-ray diffraction diagram of a raw zircon sand.

5 is an X-ray diffraction diagram of stabilized zirconia prepared according to the preparation method of the present invention.

6 is a graph showing the change in the silicon impurity content with heating time in the stabilized zirconia prepared according to the production method of the present invention.

* Explanation of symbols for main parts of the drawings

1: briquette, 2: melt,

3: plasma, 4: cooling water circulation,

5: gas flow part, 6: tungsten rod (cathode),

7: copper nozzle (both countries), 8: copper crucible (both countries).

The present invention relates to a method for preparing stabilized zirconia (FSZ: cubic ZrO ₂ ) from zircon (ZrSiO ₄ ) sand, and more specifically, after mixing carbon as a reducing agent and CaO as a stabilizer in a zircon sand, The present invention relates to a method for producing stabilized zirconia by heating and melting metal.

Zirconia (ZrO ₂ ) in monoclinic or tetragonal systems is used as an important heat-resistant material due to its chemical stability, high melting point, and low coefficient of thermal expansion. However, near 1,200 ℃, due to the large volume change (about 7.5%) caused by phase transformation of monoclinic ↔ tetragonal system, the material is destroyed, so pure zirconia of monoclinic or tetragonal system is suitable as high temperature refractory material above 1,200 ℃. Not. Therefore, stabilizer zirconia is produced by adding a solid solution such as CaO to zirconia (ZrO ₂ ) and using it as a high temperature heat-resistant material. Such stabilized zirconia is widely used as a high temperature material because it exists in a cubic system without phase transformation even when heated above 2000 ° C.

The production method for producing stabilized zirconia from zircon sand can be broadly classified into a wet method and a dry method. In the wet method, as shown in FIG. 1, a stabilizer is added to the zirconium acid salt (ZrOCl ₂ · 8H ₂ O) obtained by first treating zircon ore by alkali melting, etc., followed by heating to hydrolyze or a mixture thereof. A method of producing stabilized zirconia by filtration and washing the material produced by neutralization with ammonia hydroxide (NH ₄ OH) and calcining them.

However, this method is able to obtain stabilized zirconia with relatively high purity, but the process is complicated and the recovery rate is not good, and a large amount of acid and alkali are used during the purification process, so that waste acid and waste alkali are generated. It may cause environmental pollution.

On the other hand, as a dry method, there is a melting method, which is a method of producing stabilized zirconia by adding a stabilizer to the zircon ore and heating in an electric arc, etc. to volatilize and remove SiO ₂ and to recover the remaining ingot. . However, this method is not only difficult to manufacture high quality stabilized zirconia, but also takes a long time at a high temperature, which is economically difficult.

Conventional methods for producing stabilized zirconia from zircon sand as described above have a problem in that the manufacturing process is complicated in the wet method or waste liquid such as waste acid or waste alkali occurs during the manufacturing process, and environmental pollution is a concern. Not only is it difficult to produce stabilized zirconia but there are also uneconomical problems. Accordingly, the present inventors have conducted research and experiments to solve the problems of the conventional methods described above, and suggest the present invention based on the results. An object of the present invention is to provide a method for producing stabilized zirconia using thermal plasma that does not generate environmental pollutants.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

In the present invention, a CaO stabilizer and carbon are added to the zircon sand so that the molar ratio of CaO / zircon sand is 0.5 or more, preferably 0.5 to 0.8, and the molar ratio of carbon / zircon sand is 1.0 or more, preferably 1.0 to 4.0. Mixing step; Preparing the mixed mixture as briquettes as described above; It relates to a method for producing stabilized zirconia from zircon sand comprising the step of heating and melting the briquettes by hot thermal plasma, and then recovering and pulverizing the produced solid product.

Hereinafter, the present invention will be described in detail with reference to FIGS. 2 and 3.

In order to prepare stabilized zirconia from zircon sand according to the present invention, as shown in FIG. 2, a CaO stabilizer is added to the zircon sand so that the molar ratio of CaO / zircon sand is 0.5 or more and the molar ratio of carbon / zircon sand is 1.0 or more. Briquettes are prepared by mixing carbon.

The carbon molar ratio of 1.0 or more is because when the carbon molar ratio is 1.0 or less, it is difficult to volatilize and remove all SiO ₂ components in the zircon sand, so that the purity of the stabilized zirconia obtained is very low. When the briquette is heated and melted by thermal plasma, rapid heating by plasma and strong stirring by plasma gas are accompanied, so that some of the carbon does not participate in the reaction and is scattered and removed. By selecting suitably, the purity of the stabilized zirconia produced becomes high. However, in too many cases, raw material and energy losses are involved, so in terms of economical and stabilized zirconia purity, the upper limit of the molar ratio is preferably set to 4.0.

Even when the molar ratio of CaO / zircon sand is 0.5 or less, if all added CaO participates in the reaction without scattering, cubic zirconia, that is, stabilization zirconia may be obtained, but usually rapid heating by plasma and strong stirring by plasma gas Accompanied by partial scattering and removal, only monoclinic and tetragonal zirconia are formed or cubic, monoclinic, and tetragonal systems appear to be mixed. In addition, when the molar ratio of CaO / zircon sand is 0.8 or more, calcium zirconate (CaZrO ₃ ) or the like may be formed, so the molar ratio of CaO / zircon sand is more preferably limited to 0.5 to 0.8. In addition, the reason why briquettes are melted before melting by heat plasma is to suppress the scattering of the mixture by plasma gas during treatment by high temperature heat plasma. It can be effectively suppressed.

The briquettes prepared as described above are heated and melted for ₂ to 7 minutes, more preferably for 3 to 5 minutes, by a high temperature thermal plasma as shown in FIG. 3, and the SiO ₂ component is reduced to SiO form to volatilize and remove Ca. The component reacts with the zirconia component to form stabilized zirconia.

The process of heating and melting briquettes by high temperature thermal plasma is as follows.

That is, as shown in FIG. 3, the briquette 1 prepared as described above is charged into a water-cooled copper crucible 8, and then a tungsten rod (cathode) 6 and a copper grate (anode) ( 7) Ar gas is introduced through the gas flow section 5 while generating arc, thereby generating a plasma (3). The plasma (3) melts the briquettes in the water-cooled copper crucible (8) to melt the melt (2). ) During the melting operation, the cooling water is circulated through the cooling water circulation unit 4 through the negative electrode 6 and the positive electrode 7, and the cooling water is circulated through the water freezing crucible.

This method is different from the conventional dry method in that Ar gas is flowed between the cathode and the anode inside the plasma torch for the generation of plasma. It is strongly sprayed on the molten sample to stir the molten sample to give a homogeneous reaction throughout the sample and to drastically lower the concentration of SiO and CO on the gas side in the liquid / gas reaction layer in the molten sample to promote rapid release of the generated gas. In the end, it is to rapidly promote the reaction of stabilizing zirconia. In addition, as a reaction product obtained by cooling the melt produced after such a high temperature reaction, only stabilized zirconia is produced, and zirconium carbide generated by carbon reduction of conventional zircon sand is not produced. In addition, the stabilized zirconia produced by the present invention can be used by grinding and sizing at the appropriate particle size according to the use.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

The mole ratio of carbon and CaO to the US zircon sand having the chemical composition and component ratio shown in Table 1 and showing the X-ray diffraction model as shown in FIG. After the mixing in the ratio of 0.3 to 0.8: 1, briquettes were prepared. As can be seen in FIG. 4, a small amount of monazite is contained in the zircon sand.

TABLE 1

Each briquette was charged into a water-cooled copper crucible used as a positive electrode of a 90 Kw plasma reactor, and then heated and melted for 1 to 5 minutes by an ultra high temperature plasma.

The sample melted and heated for about 3 minutes by a plasma apparatus was cut off by power, cooled, taken out and pulverized, and each of them was subjected to diffraction analysis by X-ray diffraction analysis. . As shown in FIG. 5, when the compounding ratio is (2 carbon): (0.3CaO): (1 zircon), it can be seen that monoclinic and tetragonal zirconia are formed as a product obtained by heating experiment. However, when the compounding ratio of CaO is 0.5 and 0.8, it turns out that only cubic zirconia, ie, stabilized zirconia, is produced. Therefore, X-ray diffraction analysis confirmed that unreacted zircon sand, calcium zirconate and zirconium carbide produced by the conventional carbon method were not produced.

In order to know the change of Si content according to the heating time and the mixing ratio of carbon, CaO and zircon samples by plasma, the result of chemical analysis of the produced solids after melting is shown in FIG. 6, as shown in FIG. In the case where the compounding ratio is (3 carbon): (0.8CaO): (1 zircon), it can be seen that the Si content is rapidly decreased as the heating time increases. This tendency coincides with the tendency of adding only carbon to zircon sand when heated and melted by plasma, and similar trends are expected in other carbon compounding ratios.

Also, as shown in FIG. 6, when the CaO content is constant, as the carbon content increases, the impurity Si content in the stabilized zirconia tends to decrease.In the same carbon content, the impurity Si content increases as the CaO content increases. It can be seen that there is a characteristic.

As described above, in the present invention, since the removal reaction of SiO ₂ impurities proceeds rapidly by the participation of the reaction between the ultra-high temperature obtained by the plasma device and the plasma gas, the high temperature reaction time is less than that of the conventional electrolytic method, and the heating is performed. Since zirconia is obtained directly after melting, the manufacturing process is simpler than conventional methods, such as not undergoing baking at high temperature.

Claims (1)

Adding and mixing CaO stabilizer and carbon to the zircon sand such that the molar ratio of CaO / zircon sand is 0.5 to 0.8 and the molar ratio of carbon / zircon sand is 2.0 to 4.0; Preparing the mixed mixture as briquettes as described above; Method of producing a stabilized zirconia from zircon sand characterized in that it comprises the step of heating and melting the briquette by hot plasma for 2 to 7 minutes and then recovering and pulverizing the solid product produced.